1. Field of the Invention
The present invention relates to fermentation processes and fermentation medium compositions, and in particular to processes for producing fermentation products under conditions that thermodynamically favor production of the fermentation products.
2. Background
Bioproducts and biofuels are organic compounds made from recently living organic matter. Biofuels present the possibility of capturing and storing solar energy in a cost effective and environmentally sustainable manner. In addition, waste biomass that would otherwise be stored in landfills can be converted to biofuels. Bioproducts can also displace the need for fossil fuels to produce such products as plastics.
Currently ethanol made from corn grain is the main biofuel produced in the U.S. Alternatively, methane is made from animal manure and burned for heat or electricity. Methane is a one-carbon alkane. These two options currently provide a limited amount of fuel at a low level of efficiency. Acetic acid used in many industrial applications is made from fossil fuel or from the ethanol in wine or cider. Carboxylic acids like acetic acid, propionic acid, butyric acid and others could be used to make alcohols, alkanes, or polymers if the cost of their production could be kept low enough. Currently, lactic acid is made from sugar or starch, and it is used to produce a bio-plastic. Wherein many of these organic compounds are produced from fossil fuels, or from expensive sources of biomass like sugar or starch, a means to make various bio-products from inexpensive sources of biomass like plant fiber is needed.
If bioproducts and biofuels could be inexpensively produced from plant fiber, waste biomass like leaves, paper, manure, wood byproducts, and others could offset fuel shortages. Plant fiber, also called cellulosic biomass because it contains cellulose, can be grown on marginal land and in greater yields than grain crops. Eventually, the U.S. aims to use up to a billion tons of such biomass per year. However, there are few processes available to breakdown plant fiber comprised of cellulose, hemicellulose, pectin, and lignin. Many of these processes are inconvenient or expensive because of the difficulty in degrading plant cell wall. There is a need to further increase the rate and extent of plant fiber digestion to produce bioproducts.
The microorganisms that live in the first stomach chamber, or rumen, of cattle and other ruminants can readily degrade plant cell wall but they produce a mixture of acids rather than specific bioproducts. Other sources of microorganisms like animal feces, insect gut, or compost also produce a mixture of organic acids or methane but not high concentrations of specific carboxylic acids, alcohols, or longer-chain alkanes. Previous disclosures by the inventor (U.S. Ser. No. 60/870,441; U.S. Ser. No. 12/000,856; U.S. Ser. No. 61/113,337; U.S. Ser. No. 12/385,215; U.S. Ser. No. 61/165,654) describe production of acids, alcohols, methane, or hydrogen from biomass using fermentation, and the use of thermodynamics to shift fermentation profiles toward desired products. However, there is a need to produce additional products.
Synthesis gases (CO2, CO and H2) can be produced as byproducts of fossil fuel or biofuel production or from heating of biomass to high temperatures with limited oxygen. Thus, it may also be advantageous to make bioproducts like alcohols, alkanes or acids from such gases. Previous disclosures (U.S. Ser. No. 61/165,654; PCT/US2010/029707) describe methods to convert gases into alcohols, specific acids, or methane, and the use of thermodynamic analysis to shift fermentation toward desired products and to produce higher concentrations of desired products.
An alternative to ethanol from corn grain or methane from animal manure would be to produce various hydrocarbons (e.g. alkanes, alkenes, and alkynes) from different types of biomass. Hydrocarbons may range in size with the short-chain hydrocarbons being gaseous at room temperature and long-chain hydrocarbons being liquids at room temperature. Currently most hydrocarbons are produced from fossil fuels. Alkanes greater in length than one-carbon are generally understood to derive from fossil degradation of biomass under high pressures and temperatures. It would be advantageous to produce hydrocarbons greater than one carbon in length through microbial digestion and fermentation. An advantage of hydrocarbon production over ethanol or methane is that longer-chain hydrocarbons would be separated easily from the liquids in which they are produced, and they would be more easily condensed or compressed than methane. For example, propane is a gas that would bubble from fermentation liquid, but can be readily compressed to liquid propane gas. Higher chain-alkanes like hexane or octane could be separated readily from liquids and used to extend gasoline. Thus, it would be advantageous to produce alkanes from various sources of biomass or from synthesis gases (CO2, CO, H2).
Hydrocarbons greater in length than one-carbon are generally understood to derive from fossil degradation of biomass under high pressures and temperatures and millions of years time. Only a few microorganisms have been discovered that produce trace quantities of certain alkanes. One may contemplate genetic engineering approaches to develop organisms that convert a large quantity of some type of biomass, such as a sugar or plant fiber, or to convert synthesis gases, to hydrocarbons. These organisms may be developed by first isolating organisms that produce trace quantities of hydrocarbons, and then identifying metabolic pathways that produce the hydrocarbons. The genes encoding the enzymes in those pathways may then be inserted into the genome of a convenient host organism and through known genetic engineering techniques those genes may be turned on. However, even though genetic engineering approaches are now facilitated by current technologies, developed organisms often do not survive well, or compete well against mutants or contaminant organisms. The resultant organisms often do not produce the desired products even when the enzymes are present.
Previous disclosures by the inventor (U.S. Ser. No. 60/870,441; U.S. Ser. No. 12/000,856; U.S. Ser. No. 61/113,337; U.S. Ser. No. 12/385,215; U.S. Ser. No. 61/165,654; PCT/US2010/029707) describe using mathematical models based on the second law of thermodynamics to define conditions that determine which products are produced in a fermentation process and to accelerate the digestion and fermentation process. For example, the simplest alkane, methane, can be made to evolve more quickly by removing fermentation gases to decrease the partial pressures of gases in the fermentation. Likewise, more alkyl alcohols can be produced through fermentation by manipulating the concentrations and the ratios of concentrations of products and reactants to make the desired products more thermodynamically favorable. It would be advantageous to apply the same approach to produce other organic compounds such as hydrocarbons from biomass or synthesis gases.